1. Field of the Invention
The present invention relates to a small current sensor capable of sensing with high sensitivity a change in the current flowing through a conductor.
2. Description of the Related Art
Generally, as a way to accurately sense a weak control current flowing through a circuit of control equipment, resistors are connected in series in the circuit and a voltage drop in the resistors is measured. In this way, however, a load different from that in a control system is applied, which might exert an influence on the control system. For this reason, there is employed an indirect measuring method in which the gradient of a magnetic field generated by a control current is detected. Specifically, a line to be measured is wound around a toroidal core, and a control current is then supplied to the line measured, thereby detecting a magnetic flux generated in the center portion of the toroidal core by Hall element.
However, problems with such a current sensor employing the above method such as the difficulty of miniaturization and the insufficiency of linearity or high frequency responsiveness have been pointed out. For this reason, a current sensor has been proposed in which a giant magnetoresistive element (hereinafter referred to as a GMR element) that produces giant magnetoresistive effect is disposed in a magnetic field in order to detect the gradient (see, for example, U.S. Pat. No. 5,621,377). A current sensor using such a GMR element can improve detection sensitivity and responsiveness, and also exhibit detection characteristics that are stable against temperature changes.